Recently, along with improvement in silence of vehicles, since contribution to vehicle noises due to rotation of pneumatic tire with load is large, reduction thereof is required. Among such noises, tire noises having a high frequency, in particular, around 1000 Hz, are a main cause of vehicle exterior noises, and measures for reduction thereof is required for solving environment problems.
This tire noise around 1000 Hz is mainly generated by air-column resonance. Air column resonance sound refers to a noise generated by resonance of air inside a tube surrounded by a circumferential groove extending continuously in a tread circumferential direction, and a tread surface, and is usually observed within a range of around 800 to around 1200 Hz in ordinary passenger vehicles, and is a majority of noises generated from pneumatic tires due to a high peak sound pressure level and a wide frequency band. Moreover, since human hearing is especially sensitive to a frequency band around 1000 Hz, reduction of such air column resonance sound is effective as well in view of improvement in silence when travelling on a feeling surface.
Here, as a pneumatic tire having reduced air column resonance sound, suggested are, e.g., a pneumatic tire having a resonator disposed on a land portion partitioned by a circumferential groove, the resonator having an air chamber opening toward a land portion surface, and having one narrow neck connecting the air chamber to the circumferential groove (e.g., PTL 1), and a pneumatic tire having a resonator disposed on a land portion partitioned between two circumferential grooves, the resonator having an air chamber opening toward the land portion, one or more narrow necks connecting the air chamber to one circumferential groove of two circumferential grooves, and one or more narrow necks connecting the air chamber to the other circumferential groove (e.g., PTL 2), etc. According to the former pneumatic tire, by disposing a resonator, it is regarded as possible to reduce air column resonance sound generated in the circumferential groove; further, according to the latter pneumatic tire, comparing to the resonator having narrow necks opening toward the one circumferential groove according to the former pneumatic tire, it is possible to simultaneously reduce air column resonance sound generated in the two circumferential grooves. Therefore, it is regarded possible to effectively reduce air column resonance sound, reduce the number to dispose resonators, and thus possible to prevent deterioration of land portion rigidity.